Abstract: Objective To study the cytotoxicity of hydroquinone(HQ)on normal ratepidermal keratinocytes in vitro.Methods Keratinocytes were treated with HQ of 0,1,215,5,10 and 25μg/ml.The cell proliferation,lactate dehydrogenase (LDH)release,reactive oxygen species(ROS)level,malondialdehyde(MDA)content and activity of glutathione peroxide (GSH-Px)and superoxide dismutase(SOD)in keratinocyte were detected respectively.Results HQ could induce a dose and time-dependent decrease in cell viability.A time and concentration-dependent release of LDH was observed after cells were exposed to 0,1,215,5,10 and 25μg/ml HQ.When the same concentration HQ treated keratinocytes for 12 h,HQ also induced an increase of ROS intensity and MDA content,while an inhibition of SOD and GSH-Px activity in a concentration dependent manner.The lowest concentration were 5μg/ml and 215μg/ml,respectively.Compared withthe control group,the variance was significant(P<0.05,P<0.01).Conclusion The results suggest thathQ could induce cytotoxicity to cultured rat epidermal keratinocyte in vitro,which was associated withlipid peroxidation and oxidative stress.